The present invention relates to a thin-film yoke magnetoresistive head (`a yoke thin film magnetic head` is referred to as a YMR head hereinbelow) which is provided with a magnetoresistive element (`a magnetic resistance effect element` is referred to as an MR element hereinbelow) applying the magnetoresistive effect of a ferromagnetic thin film so as to detect the magnetic flux of signals recorded onto a magnetic recording medium.
As shown in FIG. 19, a known YMR head is comprised of a first insulation layer 52 formed on a substrate 51 having high permeability, a conductor 54 to apply bias magnetic field to an MR element formed on the first insulation layer 52, a second insulation layer 53 covering the conductor 54, an MR element 55 placed on the second insulation layer 53, a gap insulation layer 56 so formed as to cover all of the MR element 55, the second insulation layer 53 and the first insulation layer 52, a first yoke 57 and a second yoke 58. The YMR head is placed adjacent to a magnetic recording medium 59.
For the yokes 58 and 57 formed on the gap insulation layer 56, sputtered Ni-Fe films are employed because of their readiness for property control, their superior productivity and magnetic properties enjoyed in the case where a step difference is present in the substrate 51, etc.
In general, however, the sputtered Ni-Fe films referred to above cannot display satisfactory magnetic properties unless they are applied with high negative substrate bias when sputtered (with reference to I.E.E.E TRANSACTION ON MAGNETIC, VOL. MAG-15, NO. 6 (1979) P.1821 "Structure-sensitive Magnetic Properties of RF Sputtered Ni-Fe Films"). In other words, if the substrate biasing voltage is low, the direction of the easy axis of the sputtered films is vertical to the film surface. Moreover, in the case where no negative substrate bias is applied during sputtering, it is necessary that the target voltage should be high to increase the energy of particles incident on the substrate. Accordingly, a residual compressive stress in the sputtered Ni-Fe films increases due to the peening effect in any of the aforementioned manners. The residual stress in the magnetic thin film constituting the first and second yokes 57 and 58 remains even after the thin film is processed into the shape of a yoke. As a result of reaction to the residual internal stress in the yokes 57 and 58, it induces stress in the MR element 55. The induced stress in turn gives rise to a magnetic anisotropy within the MR element 55, which fact disturbs the magnetic anisotropy naturally induced to the MR element when the MR element 55 is evaporated. This anisotropy dispersion in the MR element 55 results in discontinuities of the magnetization curve inside the MR element 55, thereby giving rise to the generation of Barkhausen noises. Thus, as described above, the residual stress in the yokes has a bad influence on the characteristic of YMR head and therefore, it has been strongly desired to hold the internal stress to as small an amount as possible. However, since it is difficult to reduce the residual compressive stress of the sputtered film itself such as sputtered Ni-Fe film, it has been disadvantageous that Barkhausen noises are inevitably generated when the sputtered Ni-Fe film is used for the yoke material.